Report on a focus of onchocerciasis in Esmeraldas province of Ecuador

Elimination of onchocerciasis in Ecuador: findings of post-treatment surveillance

BACKGROUND

The Esmeraldas focus of onchocerciasis in Ecuador expanded geographically during the 1980s and was associated with severe ocular and skin disease. Mass drug administration (MDA) with ivermectin started in 1991, initially once but later twice a year, in the principle endemic focus followed by all satellite foci. Treatment was stopped in 2009 when entomological assessments determined that transmission of Onchocerca volvulus had been interrupted.

METHODS

Three years after the cessation of ivermectin treatment in 2012, as defined by the WHO guidelines for onchocerciasis elimination, blackfly collections were done in four sentinel sites in former hyperendemic areas. The presence of infective larvae in local vectors, Simulium exiguum and Simulum quadrivittatum, was assessed by detection of O. volvulus DNA by PCR. Additional flies captured in four extra-sentinel sites located in former hyper- and mesoendemic dispersed isolated areas were also assessed.

RESULTS

The results from 68,310 captured blackflies, 40,114 from four sentinel villages in the previously hyperendemic areas (Corriente Grande, El Tigre, San Miguel on Río Cayapas and Naranjal on Río Canandé) and 28,197 from extra-sentinel locations, were all negative for the presence of O. volvulus. These extra-sentinel sites (Hualpí on Río Hoja Blanca, Capulí on Río Onzole, La Ceiba on Río Tululví and Medianía on Río Verde) were included to provide additional evidence of the impact of MDA on the transmission of O. volvulus in isolated endemic areas.

CONCLUSIONS

Our data indicate that transmission of O. volvulus has been stopped in all endemic areas in Ecuador, including all satellite foci outside the main focus. These findings indicate that a strategy of ivermectin distribution twice a year to over 85% of the treatment-eligible population was effective in eliminating the infection from Ecuador in a focus with a highly competent primary vector, S. exiguum, and where the infection rates were equal to or greater than observed in many onchocerciasis foci in Africa.

Interruption of infection transmission in the onchocerciasis focus of Ecuador leading to the cessation of ivermectin distribution

Introduction: A clinically significant endemic focus of onchocerciasis existing in Esmeraldas Province, coastal Ecuador has been under an ivermectin mass drug administration program since 1991. The main transmitting vector in this area is the voracious blackfly, Simulium exiguum. This paper describes the assessments made that support the decision to cease mass treatment.

Methodology and Principle Findings: Thirty-five rounds of ivermectin treatment occurred between 1991–2009 with 29 of these carrying >85% coverage. Following the guidelines set by WHO for ceasing ivermectin distribution the impact on parasite transmission was measured in the two vector species by an O-150 PCR technique standard for assessing for the presence of Onchocerca volvulus. Up to seven collection sites in three major river systems were tested on four occasions between 1995 and 2008. The infectivity rates of 65.0 (CI 39–101) and 72.7 (CI 42–116) in 1995 dropped to zero at all seven collection sites by 2008. Assessment for the presence of antibodies against O. volvulus was made in 2001, 2006, 2007 and 2008 using standard ELISA assays for detecting anti-Ov16 antibodies. None of total of 1810 children aged 1–15 years (between 82 and 98% of children present in the surveyed villages) tested in the above years were found to be carrying antibodies to this antigen. These findings were the basis for the cessation of mass drug treatment with ivermectin in 2009.

Significance: This fulfillment of the criteria for cessation of mass distribution of ivermectin in the only known endemic zone of onchocerciasis in Ecuador moves the country into the surveillance phase of official verification for national elimination of transmission of infection. These findings indicate that ivermectin given twice a year with greater than 85% of the community can move a program to the final stages of verification of transmission interruption.

Onchocerciasis has been known to be endemic in the northwestern coastal riverine jungle areas of the country since the early 1980's. A mass drug administration program with ivermectin was implemented in 1991, and in recent years has included consistent twice a year treatment. The impact of this program, and progress towards eliminating the transmission of Onchocerca volvulus from the endemic zone, was assessed by studying entomological parameters at sentinel sites in 1995, 2000, 2004 and 2008 using PCR detection of infective larvae in the vectors (Simulium exiguum and Simulium quadrivittatum); the survey of 2008 showed that all of the collection sites had reached a level consistent with the interruption of transmission. Serological assessment of children and adolescents in 2001–2008 also showed that transmission had been interrupted. These findings support the contention that the Ecuadorian Program has reached the post-treatment surveillance phase of the elimination program; mass drug administration _{of ivermectin was consequently stopped.} The factors contributing to this successful achievement include ivermectin coverage of consistently around 85% or greater since 1998, careful consideration and control of possible expansions of the endemic area through migration, and the maintenance of a strong community health programme.

Onchocerciasis in Ecuador: evolution of chorioretinopathy after amocarzine treatment

AIMS

To investigate the impact of the macrofilaricidal drug, amocarzine, on the evolution of chorioretinopathy in onchocerciasis.

METHODS

A prospective uncontrolled cohort study was performed using subjects infected with Onchocerca volvulus in a hyperendemic onchocerciasis focus in Esmeraldas Province in Ecuador. Study subjects were recruited into four cohorts in which ophthalmic and parasitological data were collected for 2, 3, 4, and 5 years respectively.

RESULTS

Complete ophthalmic follow up was obtained for 294 individuals in the four cohorts. The incidence of retinal pigment epithelial atrophy tended to remain constant between cohorts while that of chorioretinal scarring with a greater observation period. The incidence rate of cases with new or extending chorioretinal lesions was greater with an increasing period of follow up. An association was seen between the cumulative microfilarial loads in the skin and the development of new chorioretinal lesions (p < 0.05). No relation was noted between cumulative microfilarial loads and the progression of existing disease.

CONCLUSION

Amocarzine therapy did not prevent the natural evolution of chorioretinal disease. It was suggested that ocular microfilariae were necessary for the induction of chorioretinopathy in previously unaffected eyes and that extension of existing disease might also be related to the presence of ocular microfilariae or to other immunological mechanisms.

Onchocerciasis in Ecuador: changes in prevalence of ocular lesions in Onchocerca volvulus infected individuals over the period 1980-1990

Trends in prevalence rates of onchocercal ocular lesions were examined over the period 1980 to 1990 using data from two cross-sectional surveys. There was evidence for increasing prevalence of anterior chamber microfilariae, iridocyclitis, optic atrophy, and chorioretinopathy. Large increases in prevalence, in particular, were seen for posterior segment lesions: optic atrophy increased from 2.7% to 6.4% and chorioretinopathy from 8.8% to 35.6%. Greatest increases in these lesions were seen in the Chachi which was attributed to the large increases in prevalence of microfilariae in the anterior chamber particularly in those aged 30 years or greater. The study findings suggest that ocular onchocerciasis is evolving in parallel with the well documented parasitological changes.

Onchocerciasis in Ecuador: ocular findings in Onchocerca volvulus infected individuals

Little is known of the epidemiology and clinical picture of ocular onchocerciasis in South America. A survey of onchocercal eye disease was performed in the hyperendemic area of a rain forest focus of onchocerciasis in Esmeraldas Province in Ecuador. A total of 785 skin snip positive individuals from black and Chachi Amerindian communities were examined. The blindness rate attributable to onchocerciasis was 0.4%, and 8.2% were visually impaired. Onchocercal ocular lesions were seen in a high proportion of the study group: 33.6% had punctate keratitis, microfilariae in the anterior chamber and cornea were seen in 28.9% and 33.5% respectively, iridocyclitis was seen in 1.5%, optic atrophy in 5.1%, and chorioretinopathy in 28.0%. Sclerosing keratitis was not seen. The prevalence of all ocular lesions increased with age. Punctate keratitis was strongly associated with microfilarial counts in the cornea and chorioretinopathy was correlated with infection intensities in the cornea and anterior chamber. Chachi Amerindians had higher anterior chamber microfilarial counts and a greater prevalence of punctate keratitis than blacks though blacks had a greater prevalence of iridocyclitis and optic nerve disease. The pattern of ocular disease resembled rain forest onchocerciasis in west Africa with few severe ocular lesions in the anterior segment and all blinding lesions attributable to posterior segment disease.

Intestinal helminthiases in Ecuador: the relationship between prevalence, genetic, and socioeconomic factors

Prevalence of infection with the intestinal helminths, Ascaris lumbricoides, Trichuris trichiura, Ancylostoma duodenale and Strongyloides stercoralis was examined in 632 residents of communities in Esmeraldas Province of Ecuador. These communities were divided into two groups according to area of habitation which reflected different socioeconomic circumstances. Attempts were made to correlate infection status with race and ABO blood group phenotype. The racial groups included blacks, Chachi amerindians, and mixed-race mestizos. Greater prevalences of infection were seen in the area of lower socioeconomic status. No racial or blood group associations with helminth infection were seen controlling for socioeconomic status.

Uptake of chloroquine by Onchocerca volvulus in vivo and in vitro

Patients infected with Onchocerca volvulus in the Cayapa River focus in north-east Ecuador were given 500 mg chloroquine diphosphate (CQ) orally prior to nodulectomy. The concentrations of CQ were determined in parasite fragments and host tissue dissected from the nodules, in skin overlying the nodules, and in plasma at 3, 4, 7, and 24 hours after dosing. Onchocerca volvulus took up CQ rapidly, in some cases accumulating the drug to concentrations of over 600 pmol mg-1 worm tissue by three hours, and maintaining similar concentrations through 24 hours. These amounts were markedly higher than peak concentrations in plasma (3.16 pmol microliters-1) and in host tissues (78 pmol mgm-1) and skin (up to 93 pmol mg-1). In vitro uptake of CQ by females of O. volvulus was greater under alkaline conditions (pH 8.4) than at pH 6.8 and 7.4. Uptake reached equilibrium after one to two hours, with final concentrations being approximately 10 times lower than those reached in vivo. Inhibitory effects of chloroquine and its major metabolite desethylchloroquine on the motility of O. volvulus and other filariae have been observed previously in vitro; whether or not the drug had adverse effects on adult parasites in vivo was not determined in these experiments. However, the results illustrate the accessibility of O. volvulus to blood borne agents in vivo, and the potential importance of pharmacodynamic characteristics in the search for new macrofilaricidal agents.

Onchodermatitis--correlation between skin disease and parasitic load in an endemic focus in Ecuador

Onchocerciasis is a chronic parasitic infection in which infiltration of the skin by microfilariae has been associated with a number of different pathological changes. This survey compared the prevalence of different forms of skin disease in two villages, one of which was located within the endemic zone for onchocerciasis (Zapallo Grande), in a lowland rain forest area of western Ecuador. The commonest skin diseases in both villages were scabies, pyoderma and pityriasis versicolor. In addition changes closely correlated with the presence of microfilariae in skin snips were found in Zapallo Grande--such as atrophic gluteal changes, and acute and chronic papular dermatitis. The only other skin disease associated with onchocerciasis was widespread tinea corporis due to T. rubrum. The Amerindians in the endemic onchocerciasis area were more likely than Negroes to have generalized atrophic changes of the skin, whereas in the latter group significant numbers of individuals had no obvious skin lesions but large numbers of microfilariae were detected in skin snips. Acute papular dermatitis was common in both groups and in biopsied lesions microfilariae could usually be identified within the epidermis or close to the dermo-epidermal junction. One patient had developed severe reactive onchodermatitis (Sowda). Swabs taken from onchocercal skin lesions showed no evidence of skin surface carriage of Staphylococcus aureus. Changes classically associated with onchocerciasis such as pretibial hypopigmentation (leopard skin) and hanging groin were notably absent in this population.

Studies on the biology of Simuliidae (Diptera) at the Santiago onchocerciasis focus in Ecuador, with special reference to the vectors and disease transmission

A survey showed the presence of seven simuliid species in the onchocerciasis focus in Ecuador Simulium exiguum and S. quadrivittatum were the two most common anthropophilic species and were shown to be both experimental and natural vectors of Onchocerca volvulus. S. antillarum only occasionally bit man. Observations were made on the biology of the two vector species and it was evident that S. exiguum was the primary vector of onchocerciasis in the rainy season. The relevance of these findings to the epidemiology and control of onchocerciasis in Ecuador are discussed.

Onchocerciasis in Ecuador, IV. Comparative studies of the disease relating to the Chachi and black populations in the province of Esmeraldas

The frequency, intensity and clinical features of onchocerciasis in the two ethnic groups (Blacks and Chachilla--an indigenous tribe) in the endemic foci of the disease in Esmeraldas province (Ecuador) were evaluated. The incidence of infection and intensity of the disease seen in both groups were directly related to the frequency of man-vector contact and not to racial factors. Both groups showed the same rate of positivity in both the hyperendemic and hypoendemic areas. Males of both groups had a consistently higher positivity rate than did females. The Chachilla were found to have a higher mean microfilarial density than Blacks in both types of endemic areas. Certain clinical features of the disease analogous to those seen in the African form were present only in Blacks. No lymphatic involvement or hypertrophic scarring was seen in the Chachilla, suggesting that in the Blacks there may be a generaically related predisposition to lymphatic complications of microfilarial infections.